Internal combustion engines are typically designed to operate at optimum efficiency and performance by the selection and design of a desired compression ratio, i.e., a ratio of maximum to minimum cylinder volume, during operating conditions. However, circumstances exist in which it may be desired to change a compression ratio, perhaps dynamically. For example, a compression ratio that may be desired under normal engine run conditions may not be effective during engine start conditions.
Various methods have been devised for varying the compression ratio of an engine. One such method is disclosed in U.S. Pat. No. 6,443,107, issued on 3 Sep. 2002 to Mendler (“the '107 patent”). In the '107 patent the compression ratio of the engine is varied by the use of an eccentric crankshaft cradle. When a change in compression ratio is desired, the eccentric crankshaft cradle rotates, causing the axis of rotation of the crankcase to change position. The axis of rotation of the crankshaft is moved towards or away from a top surface of the cylinder block of the engine, thereby changing the compression ratio of the engine.
One problem faced by internal combustion engines using variable compression ratio mechanisms, such as that in the '107 patent, that change the location of the axis of rotation of the crankshaft is sustaining the crankshaft in a driving relationship with the gear train of the engine. As the crankshaft is moved by the variable compression ratio mechanism, any gear mounted on the crankshaft is moved relative to the other gears of the gear train and the mesh between the gears may not be maintained. Thus, the driving relationship between the crankshaft and the gear train is interrupted.
One attempt to solve the problem of maintaining the mesh between a moving crankshaft and a stationary gear train is disclosed in U.S. Pat. No. 4,738,230, issued to Johnson on 19 Apr. 1988 (“the '230 patent”). In the '230 patent, a spur gear mounted on the crankshaft is meshed with an internal ring gear that is connected to the gear train. As the crankshaft is moved relative to the gear train, the spur gear maintains its mesh with the ring gear by moving in an arc parallel to the ring gear's pitch diameter. The gear system disclosed in the '230 patent is adequate for use on gear trains wherein the relative timing between the crankshaft and other devices driven by the gear train is not important. However, the gear system disclosed in the '230 patent is not capable of use on a gear train that drives a camshaft. As the crankshaft is moved to change the compression ratio of the engine, the crankshaft is also rotated relative to the ring gear. Therefore, the timing relationship between the crankshaft and the camshaft, which is driven by the ring gear, is not maintained. Such a disruption in timing could result in one or more of the valves of the engine colliding with a piston of the engine.
The present invention is directed to overcoming one or more of the problems as set forth above.